At first let me explain what I try to achieve. On my posts list (standard blog page) I want to add additional CSS code for the inside-article div, but only for posts of one specific category, named ‘123’. My goal is to add simple ribbon in the top left corners with CSS (I already know how to do it). I think the easiest way is to add additional CSS class, only for posts labeled with my ‘123’ category, but I don’t know how. Or maybe you have much better solution?